I'm a smiliar age and converted to Bookkeeping around 3 years ago.
I also thought about going to straight to level 4. At the time I decided to wait and get settled first.
I've still not taken the extra exams.
It really depends how far up the value chain you want to go. At level 3 you can find plenty of clients needing your skills.
If you go to level 4 you have evidence of additional skills, but in your 50's you probably have some of those skills already.
I'd advise concentrating on finding clients (and experience) with regular bookkeeping first.